1. Field of the Invention
The present invention relates to an optical transceiver used in a full duplex optical communication.
2. Related Prior Art
The current optical communication with a fully duplex function provides an optical transmitter for transmitting an optical signal converted from an electrical signal into an optical fiber, and an optical receiver for generating an electrical signal by converting an optical signal transmitted from another optical fiber. A practical optical transceiver encases these optical transmitter and receiver into a package. The Japanese Patent published as JP-2002-335215A has disclosed a light detecting circuit included within such optical transceiver.
In an optical transceiver, the optical transmitter flows relatively large current to drive a semiconductor optical device, while the optical receiver propagates a relatively small signal output from a semiconductor optical device. Accordingly, the large signal, especially a large current signal, in the optical transmitter causes a crosstalk to degrade the quality of the receiving signal converted by the optical receiver.
The light-receiving circuit disclosed in the Japanese Patent mentioned above adjusts the reference level of the comparator, to reduce the crosstalk from the optical transmitter to the optical receiver, for determining whether the input optical signal exists in the optical receiver. However, the adjustment of the reference level is carried out by a specific circuit. The crosstalk itself is an instant phenomenon; accordingly, it is quite hard to adjust instantly the reference level of the comparator synchronized with the occurrence of the crosstalk. Therefore, the circuit mentioned above would be inapplicable for the optical transceiver with the high speed operation.
The present invention is to solve the subject mentioned above, namely, to provide an optical transceiver that reduce the crosstalk from the optical transmitter to the optical receiver.